The invention relates to machines designed to apply a closing film on trays containing a product, such as a food product, provided with a sealing and cutting station with opposing bells, between which groups of trays and an overhead section of film unwound from a coil are cyclically positioned and which, on command, are reciprocally closed to heat seal a portion of covering film on the upper edge of the trays, after possible conditioning of the atmosphere inside said trays, and then to separate around the perimeter, by cutting, the cover of each tray from the off-cut of surrounding film and which, lastly, are opened to prepare for offloading of the sealed trays and to prepare for removal of the off-cut of film, usually connected to a collection axis. These machines are provided upstream of said sealing station with a station which collects together and orders groups of trays to be inserted all together into said station, downstream of which a removal conveyor and pincer means are provided to perform simultaneously, with the sealing station open, transfer of groups of open trays from the first collection station to the second sealing and cutting station and sealed trays from said station to the final removal station. The invention relates in particular to the first tray collection station and cites as the prior art patent EP 334 266, which envisages said station being formed of a conveyor with intermittent motion, which stops cyclically to await the containers which are supplied to it by the unloading conveyor of the customer's machine, which fills the trays with the product. In certain cases, the trays contain liquid products, so it is necessary to make said changes in speed of the collection belt in an extremely gradual manner, with suitable deceleration and acceleration ramps, to prevent the liquid in the trays from overflowing or soiling the upper edge of said trays, prejudicing the successful outcome of the subsequent step of heat.sealing with the covering film. In order to overcome these problems, patent EP 680 880 describes how to perform said tray collection operation without the corresponding collection conveyor having to stop cyclically. This condition is obtained by arranging a compensation conveyor between the customer's collection conveyor and supply conveyor and by providing means of detecting the distance and speed of the trays inserted on said compensation conveyor, to guide the means of motion of said conveyor, so that it inserts the trays with a predetermined speed and position on the collection conveyor, which thus no longer needs to stop in succession, as indicated in EP 334 266, with the consequent advantages.
The second solution considered above considerably extends the length of the whole collection station, complicates its construction, considerably increases its costs and reduces its technological reliability, due to the major presence of sensors and all the processing and calculation means associated with them.